There is a continuing need for analgesic medications able to provide high efficacy pain relief while reducing the possibility of undesirable effects. Non-steroidal anti-inflammatory drugs (“NSAID'S”), including compounds such as ibuprofen, ketoprofen and diclofenac, have anti-inflammatory actions and are effective on pain associated with the release of prostaglandins and other mediators of inflammation. For example, diclofenac is considered to be extremely potent and effective as an analgesic and anti-inflammatory agent. Diclofenac is approved in the United States for the long-term symptomatic treatment of rheumatoid arthritis, osteoarthritis and ankylosing spondylitis. It is also considered to be useful for the short-term treatment of acute musculoskeletal injury, acute painful shoulder, postoperative pain and dysmenorrhea. However, NSAID'S such as diclofenac produce side effects in about 20% of patients that require cessation of medication. Side effects include, for example, gastrointestinal bleeding and the abnormal elevation of liver enzymes.
The opioids are a group of drugs, both natural and synthetic, that are employed primarily as centrally-acting analgesics and are opium or morphine-like in their properties (Gilman et al., 1980, GOODMAN AND GILMAN'S, THE PHARMACOLOGICAL BASIS OF THERAPEUTICS, Chapter 24:494-534, Pub. Pergamon Press; hereby incorporated by reference). The opioids include morphine and morphine-like homologs, including, e.g., the semisynthetic derivatives codeine (methylmorphine) and hydrocodone (dihydrocodeinone) among many other such derivatives. Morphine and related opioids exhibit agonist activity at central nervous system or CNS (referring to the brain and spinal cord) μ (mu) opioid receptors as well as showing affinity for the δ and κ opioid receptors, to produce a range of effects including analgesia, drowsiness, changes in mood and mental clouding. In addition to potent analgesic effects, the morphine-related opioids may also cause a number of undesirable effects, including, for example, respiratory depression, nausea, vomiting, dizziness, mental clouding, dysphoria, pruritus, constipation, increased biliary tract pressure, urinary retention and hypotension. The development of tolerance to the opioid drugs and the risk of chemical dependence and abuse for these drugs is another undesirable effect.
Morphine, which has been considered the prototypic opioid analgesic, has been available in many dosage forms, including immediate release oral dosage forms, and more recently, formulated into 12 hour controlled release formulations (e.g., MS Contin® tablets, commercially available from Purdue Frederick Company). Other opioid analgesics have been available as immediate release oral dosage forms, such as hydromorphone (e.g., Dilaudid®, commercially available from Knoll Pharmaceuticals). More recently, another controlled release opioid analgesic, oxycodone, has become available (OxyContin®, commercially available from Purdue Pharma). There are, of course, many other oral formulations of immediate release and sustained release opioids which are commercially available throughout the world.
Prior publications report that analgesic potency may be improved while reducing undesirable effects by combining an opioid with an NSAID or an analgesic such as acetylsalicylic acid or acetaminophen, in such a way as to obtain a synergistic analgesic effect allowing for a reduction in the total dose of both the NSAID and analgesic. For example, U.S. Pat. No. 4,569,937, issued to Baker et al. on Feb. 11, 1986, describes a combination of oxycodone with ibuprofen in a ratio of oxycodone/ibuprofen from 1:6 to about 1:400. U.S. Pat. No. 4,690,927, issued to Voss et al. on Sep. 1, 1987, describes a combination of the NSAID diclofenac and codeine in a weight ratio of diclofenac to codeine of about 1:1 to about 3:1. U.S. Pat. No. 5,190,947, issued to Riess et al. on Mar. 2, 1993, describes a diclofenac-codeine salt ([2-[2,6-dichlorophenyl)-amino]-phenyl]-acetic acid). U.S. Pat. No. 4,844,907, issued to Elger et al. on Jul. 4, 1989, describes a multiphase tablet combining a narcotic analgesic phase and an NSAID phase in separate layers. U.S. Pat. No. 4,587,252, issued to Arnold et al. on May 6, 1986, describes a process for treating pain using a combination of hydrocodone and ibuprofen.
Non-steroidal, anti-inflammatory drugs (NSAID'S) exert most of their anti-inflammatory, analgesic and antipyretic activity and inhibit hormone-induced uterine contractions and certain types of cancer growth through inhibition of prostaglandin G/H synthase, also known as cyclooxygenase.
Fatty acid cyclooxygenase (COX) was described as the source of prostaglandins, thromboxanes, and a variety of other arachidonic acid-, and higher desaturated fatty acid-derived biologically active hydroxylated metabolites. Beginning in the late 1960's, B. Sammuelsson, S. Bergstrom and their colleagues discovered the biological activity and elucidated the structures of the products of cyclooxygenase. In the late 1960's and early 1970's, J. Vane discovered that aspirin and other NSAIDs exert their major biological activities by inhibiting cyclooxygenase. COX is directly responsible for the formation of PGG and PGH and these serve as the intermediates in the synthesis of PGD, PGE, PGF, PGI, and TXA. By the late 1970's and early 1980's, it was appreciated that many hormones and other biologically active agents could regulate the cellular activity of COX. At first, it was assumed that COX induction was the simple result of oxidative inactivation of COX, which happens after only a few substrate turnovers. This is common among enzymes that incorporate molecular oxygen into their substrates—the oxygen rapidly degrades the enzyme. Such enzymes are sometimes referred to as suicide enzymes. In response to the rapid (within seconds) inactivation of cyclooxygenase, its message is transcribed, and the enzyme is rapidly induced to replace that lost due to catalysis. It was noticed by several groups that cyclooxygenase was induced to a much greated degree than necessary to replace the lost enzyme. Using an oligonucleotide directed to the cloned COX-1 enzyme, a second band was identified on Northern blots under low stringency. This gene was cloned and identified as a second COX enzyme, named COX-2, and was found to be largely absent from many cells under basal conditions but rapidly induced by several cytokines and neurotransmitters. The expression of this enzyme was found to be largely responsible for the previously-observed excess COX activity in activated cells. The genes for COX-1 and COX-2 are distinct, with the gene for COX-1 being 22 kb and the message size 2.8 kb whereas the gene for COX-2 is 8.3 kb and the message size 4.1 kb. Whereas the COX-1 promoter does not contain recognized transcription factor binding sites, the COX-2 promoter contains sites for NF-κB, AP-2, NF-IL-6 and glucocorticoids (H. R. Herschman, Canc. Metas. Rev. 13: 256, 1994). There are some differences in the active sites of the enzymes. Aspirin inhibits the cyclooxygenase activity of COX-1 but leaves intact its peroxidase activity, whereas aspirin converts COX-2 from a cyclooxygenase to a 15-lipoxygenase (E. A. Meade et al, J. Biol. Chem. 268: 6610, 1993).
It has been proposed that the COX-1 is responsible, in many cells for endogenous basal release of prostaglandins and is important in the physiological functions of prostaglandins which include the maintenance of gastrointestinal integrity and renal blood flow. Inhibition of COX-1 causes a number of side effects including inhibition of platelet aggregation associated with disorders of coagulation, and gastrointestinal toxicity with the possibility of ulcerations and of hemorrhage. It is believed that the gastrointestinal toxicity is due to a decrease in the biosynthesis of prostaglandins which are cytoprotective of the gastric mucosa.
A high incidence of side effects has historically been associated with chronic use of classic cyclooxygenase inhibitors, all of which are about equipotent for COX-1 or COX-2, or which are COX-1-selective. While renal toxicity occurs, it usually becomes evident in patients who are already exhibit renal insufficiency (D. Kleinknecht, Sem. Nephrol. 15: 228, 1995). By far, the most prevalent and morbid toxicity is gastrointestinal. Even with relatively nontoxic drugs such as piroxicam, up to 4% of patients experience gross bleeding and ulcertaion (M. J. S. Langman et al, Lancet 343: 1075, 1994). In the United States, it is estimated that some 2000 patients with rheumatoid arthritis and 20,000 patients with osteoarthritis die each year due to gastrointestinal side effects related to the use of COX inhibitors. In the UK, about 30% of the annual 4000 peptic ulcer-related deaths are attributable to COX inhibitors (Scrip 2162, p. 17). COX inhibitors cause gastrointestinal and renal toxicity due to the inhibition of synthesis of homeostatic prostaglandins responsible for epithelial mucus production and renal blood flow, respectively.
The second form of cyclooxygenase, COX-2, is rapidly and readily inducible by a number of agents including mitogens, endotoxins, hormones, cytokines and growth factors.
It has been proposed that COX-2 is mainly responsible for the pathological effects of prostaglandins, which arise when rapid induction of COX-2 occurs in response to such agents as inflammatory agents, hormones, growth factors, and cytokines. A selective inhibitor of COX-2 therefore would have anti-inflammatory, antipyretic and analgesic properties similar to those of a conventional non-steroidal anti-inflammatory drug (NSAID). Additionally, a COX-2 inhibitor would inhibit hormone-induced uterine contractions and have potential anti-cancer effects. A COX-2 inhibitor would have advantages over NSAID'S such as a diminished ability to induce some of the mechanism-based side effects. Moreover, it is believed that COX-2 inhibitors have a reduced potential for gastrointestinal toxicity, a reduced potential for renal side effects, a reduced effect on bleeding times and a lessened ability to induce asthma attacks in aspirin-sensitive asthmatic subjects.
Thus, compounds with high specificity for COX-2 over COX-1, may be useful as alternatives to conventional NSAID'S. This is particularly the case when NSAID use is contra-indicated, such as in patients with peptic ulcers, gastritis, regional enteritis, ulcerative colitis, diverticulitis or with a recurrent history of gastrointestinal lesions; GI bleeding, coagulation disorders including anemia, hypoprothrombinemia, haemophelia or other bleeding problems; kidney disease, and patients about to undergo surgery or taking anticoagulants.
Once it became clear that COX-1 but not COX-2 is responsible for gastrointestinal epithelial prostaglandin production and a major contributor to renal prostaglandin synthesis, the search for selective COX-2 inhibitors became extremely active. This led very quickly to the recognition that several COX inhibitors, including nimesulide and Dup-697, which were known to cause little or no gastrointestinal irritation, are COX-2-selective.
U.S. Pat. No. 5,409,944 (Black, et al.) describes certain novel alkane-sulfonamido-indanone derivatives useful for the treatment of pain, fever, inflammation, arthritis, cancer, and other disease states. Also discussed therein are compositions for the treatment of cyclooxygenase-2-mediated diseases comprising the therein-described novel alkane-sulfonamidoindanone derivatives together with a pain reliever including acetaminophen or phenacetin; a potentiator including caffeine; an H2-antagonist, aluminium or magnesium hydroxide, simethicone, a decongestant including phenylephrine, phenylpropanolamine, pseudophedrine, oxymetazoline, epinephrine, naphazoline, xylonetazoline, propylhexedrine, or levo-desoxy ephedrine; an antitussive including codeine, hydrocodone, caramiphen, carbetapentane or dextromethorphan; a diuretic and/or a sedating or non-sedating antihistamine. While Black et al. mention the use of an antitussive dose of two opioid analgesics (codeine and hydrocodone), they do not describe or suggest the use of their COX-2 inhibitors with analgesically effective amounts of any opioid analgesics.